How does power add up in a Toyota hybrid?

[raubvogel]

Many times (and I am not able to find a single example right now) I read about the, say, Prius, it is claimed the total HP produced is 70 (engine) + 44 (electric motor) = 114. But then I see the following quote in https://blog.lexus.co.uk/history-lexus-hybrid-drive/ :

Combining the 211PS output of the petrol engine together with 167PS and 68PS from the front and rear hybrid transaxles respectively delivered a total system output of 272PS.

Well, given 211, 167, and 68, the closest I can get to 272 is by adding petrol engine to rear hybrid transaxle power ratings. So either I can't do math or...?

[Stubby79]

Probably the battery's max output plus the engine's max output.

What's the point of having motors that exceed the battery's output? It's the way the hybrid system works...the engine(through a motor-generator) will produce much of the electrical power.

Why bother? The electric motors can generate substantial torque, so you can get rid of the need for multiple gear ratios to get the most out of the engine.

This is based on my understanding of this topic...someone will come along and correct me if I'm too far off base.

[jakobnev]

You have to subtract the power MG1 uses when acting as a generator.

[Ecky]

My answer pertains to Honda hybrids but I feel their layout is more simple and easy to understand, and the same principles apply to Toyota's. I'm going to ignore any conversion losses.

Let's take the 2020 Honda Insight as an example. The drive train:
Engine - 107hp / 99ft-lbs, 6000rpm redline
Electric motor - 129hp / 197ft-lbs
Battery - 1KWh (?) lithium ion battery @ 270v nominal




There is no "transmission" as is typical in most cars. Below 60mph, the engine cannot transfer power to the wheels, period, unlike in a Volt/Prius which have planetary gearsets. Instead, the engine turns a generator. The generator and battery then send power to the electric motor. At speeds up to 60mph, it is impossible to put down more than 129hp, because only the electric motor is connected to the wheels. Floor it and the engine might rev up to redline and provide 107hp, and the battery provides the remaining energy for 22hp (~16,500w), and you get *up to* 129hp to the wheels, the max of the electric motor alone. Realistically it's going to be less, because electric motors do not produce peak HP at every RPM.

At 60mph a clutch *can* lock up and provide a single speed gear reduction between engine and wheels. Honda does this because it's lossy to convert from mechanical to electrical energy and back again, and this allows more efficient highway cruise.

I don't know what the gear ratio is for the Insight or at what vehicle speed it hits redline with the clutch locked, but let's say at 60mph the clutch locks up and the engine is at 2,000rpm. It can then produce only 1/3 of its peak HP (35.6hp). The electric motor can then provide as much "assist" as can be drawn from the battery alone, or is the max output from the electric motor at that RPM.

Given that the combined peak system output is 151hp, and the engine produces 107hp, that suggests the battery can only provide up to 44hp (151-107). 44hp = 33,000w. 33,000w / 270v = 122 amps.

So, let's say you're at 60mph and the clutch locks up and the engine can only produce 35.6hp. That suggests you can get as much as 80hp combined (35.6 + 44) at 60mph with the clutch locked (limited by the engine @ 2000rpm + battery peak output), or potentially 129hp with the clutch unlocked.

That 151hp "combined peak" can probably only happen at a particular vehicle speed, where engine/battery/motor output peaks.

[hayden55]

How exactly does the prius use its clutch?

[Ecky]

Originally Posted by hayden55

How exactly does the prius use its clutch?

To my knowledge the Prius does not have a clutch. Instead, the engine, electric motor and wheels are attached to the various parts (sun gear, orbital gears, ring gear) of a planetary gear set.

In this kind of gear set there are no frictional parts, and everything is connected via fixed gearing. Basically, no wear parts except for bearings.

The speed the ring gear turns is created by the ratio of how fast the sun gear and planetary gears are turning. The Prius thus can vary vehicle speed even while holding the engine at a fixed speed, by varying how fast the electric motor is spinning, or even by spinning it backwards. It can also vary engine speed without changing vehicle speed the same way. It's a very flexible design.

The Volt used the same design.

[cRiPpLe_rOoStEr]

The combined output lower than the sum of the powers of the engine and all the motors might have something to do with the way the electric motors act as a CVT, also considering when one of the motors serve as a generator and a higher amount of power from the ICE is resorted in order to mantain a more linear and constant performance level.

[hayden55]

Originally Posted by Ecky

To my knowledge the Prius does not have a clutch. Instead, the engine, electric motor and wheels are attached to the various parts (sun gear, orbital gears, ring gear) of a planetary gear set.

In this kind of gear set there are no frictional parts, and everything is connected via fixed gearing. Basically, no wear parts except for bearings.

The speed the ring gear turns is created by the ratio of how fast the sun gear and planetary gears are turning. The Prius thus can vary vehicle speed even while holding the engine at a fixed speed, by varying how fast the electric motor is spinning, or even by spinning it backwards. It can also vary engine speed without changing vehicle speed the same way. It's a very flexible design.

The Volt used the same design.

Ah i gotcha. I looked it up and its called a "clutch" but its actually just the damper with no friction material. From the looks its just to couple the drivetrains together with the spring plate for smooth engagement back and forth.

[raubvogel]

Originally Posted by jakobnev

You have to subtract the power MG1 uses when acting as a ge
nerator.

211 + 167 - 68 = 310 which is greater than the 272PS mentioned in https://blog.lexus.co.uk/history-lexus-hybrid-drive/. Where are the 41 horses?

Ecky, regarding the Insight, I thought its electric motor (I have one in my office and weighted in our mail scale at 43.5lb)delivered 13HP (10KW), 79Nm (58ft-lb) @ 1000rpm (https://afdc.energy.gov/files/pdfs/i...snapshot.pdf)i, but that is probably related to the earlier models. Also, I thought (https://www.insightcentral.net/KB/co...owertrain.html) there was no way to run the electric motor without the gas engine also running. Is the new model completely different than the old one? I ask because in your diagram of how the power distribution on your Insight only the electric motor is connected to the power wheels.

[Ecky]

Originally Posted by raubvogel

211 + 167 - 68 = 310 which is greater than the 272PS mentioned in https://blog.lexus.co.uk/history-lexus-hybrid-drive/. Where are the 41 horses?

Ecky, regarding the Insight, I thought its electric motor (I have one in my office and weighted in our mail scale at 43.5lb)delivered 13HP (10KW), 79Nm (58ft-lb) @ 1000rpm (https://afdc.energy.gov/files/pdfs/i...snapshot.pdf)i, but that is probably related to the earlier models. Also, I thought (https://www.insightcentral.net/KB/co...owertrain.html) there was no way to run the electric motor without the gas engine also running. Is the new model completely different than the old one? I ask because in your diagram of how the power distribution on your Insight only the electric motor is connected to the power wheels.

You're correct in that the new one uses an entirely different architecture.